The problem of loosening in service with attendant loss of clamping force, commonly encountered with threaded assemblies, is aggravated when the externally threaded member carries only a partial thread. Valve users fall prey to this problem as it is common practice to machine flats on threaded valve stems.
Prior art locknuts which bear on the thread profile suffer a significant loss of effectiveness when deprived of a full external mating thread. Although lockwashers are effective in certain applications, their use imposes minimums on clamping force; minimums which may result in undesirably high levels of compressive force applied to the finished assembly (as with a ball-valve stem and seal arrangement).